1. Field of the Invention
The present invention relates generally to a dampening solution recirculator, and, more particularly, to a dampening solution recirculator for maintaining fountain solution in a solution reservoir of a two-roller continuous type dampener.
2. Background of the Related Art
A variety of dampeners have been developed for the application of dampening solution to printing plates mounted on offset lithographic printing presses. To date, three distinct types of dampeners have emerged. The oldest type is described as a xe2x80x9cconventional,xe2x80x9d or xe2x80x9cductorxe2x80x9d type dampener. The next type is a xe2x80x9cslip-roller continuousxe2x80x9d type dampener. And, more recently, the xe2x80x9ctwo-roller continuousxe2x80x9d type dampener was developed. Those skilled in the art will appreciate that most dampeners on the market today are variations or combinations of these three types.
The conventional type dampener has a pan roller, rotating at a speed less than press speed, that picks up dampening solution from a pan style solution reservoir. The dampening solution is transferred from the pan roller to a set of dampening rollers, rotating at a speed equal to press speed, by a ductor roller that alternately contacts the pan roller and one of the dampening rollers. A printing plate, on which the image to be printed is etched, is attached to a plate cylinder. After the solution is transferred to the dampening rollers, the rollers smooth out the solution to a somewhat consistent thickness and thereafter deposit it onto the non-image areas of the printing plate. The plate cylinder then rotates the plate past the press""s inking form rollers which ink the image areas of the plate.
The slip-roller continuous type dampener also has a pan roller that rotates at a speed less than press speed and picks up the dampening solution from a pan style solution reservoir. Like the conventional system, the slip-roller continuous type dampener includes a set of dampening rollers, rotating at a speed equal to press speed, for smoothing out the dampening solution prior to the solution being applied to the printing plate. However, instead of the solution being transferred periodically from the pan roller to the dampening rollers by a ductor roller, the solution is transferred by a metering roller, which is in constant slipping-contact relationship with either the pan roller, one or both of the dampening rollers, or both the pan roller and one or both of the dampening rollers.
Both the conventional and slip-roller continuous type dampeners typically require the inclusion of 5% to 15% alcohol in the dampening solution. The alcohol reduces the surface tension of the solution; thereby enabling these type of dampeners to effectively wet the plate.
An example of a two-roller continuous type dampener is disclosed in U.S. Pat. No. 4,455,938 to Loudon, the entire disclosure of which is incorporated by reference herein. Loudon discloses a form roller having an ink receptive compressible surface pressed against a printing plate, which is attached to the plate cylinder. A metering roller presses against the form roller on a side of the form roller opposite the plate cylinder, forming a line of contact there between. The form and metering rollers rotate at a speed equal to that which the press operates and in a direction that results in the formation of an upwardly-facing inward nip. An xe2x80x9cinward nipxe2x80x9d is defined as a zone near the line of contact between two rotating rollers toward which surfaces of the rollers approach. Seals are lightly pressed against the ends of the form roller and metering roller.
The xe2x80x9ctroughxe2x80x9d created by the form roller, metering roller, and the seals form a solution reservoir in which dampening solution is stored. As the rollers in the dampener rotate, the solution is metered between the form and metering rollers and transferred to the plate by the form roller to the extent necessary to maintain the hydrophilic regions on the printing plate free of ink. The two-roller continuous type dampener has proven to be a substantial improvement over conventional and slip-roller continuous type dampeners in that it is a simpler design, easier to maintain and repair, requires only infrequent adjustments, and does not require alcohol to properly wet the plate.
In any dampener, dampening solution must be periodically replenished in the solution reservoir as it is consumed during the printing operation. The most basic method of replenishing dampening solution is by inverting a container of solution over the solution reservoir and positioning the opening of the container at a level that the solution is to be maintained. Disadvantages associated with this method include adverse chemistry changes in the solution reservoir caused by impurities, such as ink and paper dust, that migrate from the printing plate. Also, since the solution remains essentially stagnant in the reservoir, pH xe2x80x9chotspotsxe2x80x9d develop at remote locations in the reservoir. Furthermore, because the container must be positioned above and relatively nearby the reservoir, compromises must be made when choosing the size and location of the dampening solution container. Finally, such an arrangement makes it difficult to maintain and control the alcohol content of the dampening solution in those systems requiring the use of alcohol.
The advent of solution recirculators greatly improved conventional and slip-roller continuous type dampeners by eliminating many of the problems associated with inverted container type feeders. Solution recirculators typically include a housing in which a large solution storage tank is enclosed. A pump is attached to the tank for pumping solution through a supply conduit to the pan-style solution reservoir. A rigid tube extends through the bottom of the pan facilitating removal of excess solution from the pan. The level of solution in the reservoir is maintained by an adjustable collar that mates with the rigid tube on the interior of the pan. A return conduit provides fluid communication between the portion of the rigid tube extending from the bottom of the pan and the solution recirculator. The recirculator may include a chiller for lowering the temperature of the solution in the storage tank to reduce the evaporation rate of alcohol that may be included in the solution. Cooling the dampening solution has also been found advantageous for systems not requiring alcohol. Examples of solution recirculators are disclosed in U.S. Pat. No. 3,557,817 to Royse and U.S. Pat. No. 4,300,450 to Gasparrini.
One drawback inherent with prior art solution recirculating systems is that they are not adaptable to two-roller continuous type dampeners. This is primarily due to the fact that existing solution recirculators provide solution at relatively high and varying flow rates. In addition, excess solution in the reservoir is caused to return to the recirculator tank by employing gravity. In a dampener utilizing, for example, a pan type reservoir, these characteristics do not cause a problem. However, in a two-roller type continuous dampener these characteristics make solution recirculators unsuitable.
A dampener recirculator apparatus for a printing press is disclosed in U.S. Pat. No. 5,878,663 to Krzyzak et al. The recirculator apparatus makes it possible to utilize a solution recirculator with a two-roller type continuous dampener. More specifically, Krzyzak et al. disclose a dampening system that includes a two-roller continuous type dampener, solution recirculator, and a recirculator adapter. The solution recirculator is configured to supply solution through a supply conduit and to receive solution through a return conduit. The recirculator adapter includes a pressure regulator that receives solution from the supply conduit and regulates the solution flow to the dampener. A feed conduit provides fluid communication between the pressure regulator and the dampener""s solution reservoir. The recirculator adapter further includes a venturi that receives solution from the supply conduit and induces a vacuum in a suction conduit. A first end of the suction conduit is positioned at a predetermined level within the dampener""s solution reservoir and has a portion proximate the first end extending upwardly and away from the reservoir. A second end of the suction conduit is in fluid communication with the venturi. The venturi is in fluid communication with the return conduit for returning solution to the solution recirculator.
A disadvantage of Krzyzak et al. is that the recirculator adapter must be mounted on the printing press near the affected dampener. This reduces printers"" access to the dampener from the side of the printing press to which the recirculator adapter is attached. Another disadvantage is that the recirculator adapter requires a pressure regulator. Such pressure regulators add significant cost to the recirculator adapter that can make it prohibitively expensive to sell. Yet another disadvantage is that installation of the recirculator adapter requires four additional water-tight connections. Those of ordinary skill in the art well appreciate that the more connections a fluid system has, the more likely it is that a system will leak fluid.
Considering the above-described disadvantages, it is clear that there is a need in the art for an improved device or method to adapt a solution recirculator so that it may be used to provide dampening solution to two-roller continuous type dampeners.
The present invention includes a dampening solution recirculator and a method for circulating dampening solution in a reservoir of a dampener. The dampening solution recirculator includes a tank for storing dampening solution, a pump for pumping dampening solution from the tank, a venturi positioned proximate the pump and the tank and including an inlet port in fluid communication with the pump, a suction port, and a discharge port in fluid communication with the tank, a feed conduit having a first end in fluid communication with the pump and a second end positioned above the reservoir, and a suction conduit having a first end positioned at a predetermined level within the reservoir extending in a direction upwardly and away from the reservoir, and a second end in fluid communication with the suction port. The venturi may be located inside the tank and includes a venturi nozzle tapered at an angle between about 5 and 10 degrees, and preferably at an angle of about 7 degrees in relation to the axis of the venturi. The dampening solution recirculator further includes a chiller in fluid communication with the pump and the first end of the feed conduit for providing refrigerated solution to the reservoir. A filter is positioned in the tank in fluid communication with the discharge port of the venturi.
The dampener includes a bracket attached to and extending over the reservoir of the dampener. The first end of the suction conduit is mounted to the bracket. A means is provided for adjusting the bracket vertically to alter the level of dampening solution in the reservoir.
The method for circulating dampening solution in a reservoir of a dampener includes the step of providing a dampening solution recirculator that includes a tank, a pump in fluid communication with the tank, a venturi positioned proximate the pump and tank, the venturi having an inlet port in fluid communication with the pump, a suction port, and a discharge port in fluid communication with the tank, a feed conduit having a first end and a second end, the first end in fluid communication with the pump, and a suction conduit having a first end and a second end, the first end in fluid communication with the suction port. The method further includes the steps of storing dampening solution in the storage tank, positioning the second end of the feed conduit above the reservoir for feeding dampening solution into the reservoir, positioning the second end of the suction conduit at a predetermined level within the reservoir and having a portion proximate the second end of the suction conduit extending upwardly and away from the reservoir, and pumping dampening solution from the storage tank to the inlet port of the venturi and the first end of the feed conduit.
The method further includes the step of pumping dampening solution through a chiller to refrigerate the dampening solution prior to supplying the solution to the reservoir. The method further includes the steps of mounting the second end of the feed conduit and the second end of the suction conduit to a vertically adjustable bracket extending over the reservoir and adjusting the adjustable bracket to adjust the level of the dampening solution in the reservoir.
These and other features of the present invention will become more readily apparent to those of ordinary skill in the art upon a review of the following brief description of the drawings, detailed description of the preferred embodiments, and the figures appended hereto.